1. Field of the Invention
The field of art to which this invention pertains is fluid reaction surfaces having resiliently mounted nonrigid working members.
2. Description of the Prior Art
Conventional rotor systems may best be characterized by their relative complexity. The development of fully articulated rotor systems such as helicopter rotor systems has generally taken directions dictated by structural and dynamic stability requirements and the satisfaction of these requirements has resulted in rotor systems which are intricate and possess compromised weight, cost and maintenance factors. While some reduction in complexity has been achieved with nonarticulated or hingeless rotors (note, for example, U.S. Pat. No. 3,484,174), existing designs still experience relatively high blade loads and utilize such things as feathering bearings and mechanical edgewise dampers to provide pitch control and avoid destructive resonances. However, further significant reductions in weight and maintenance requirements are still possible.
Early designs (e.g., Canadian Pat. No. 951,301) of bearingless rotor systems included a "stiff" design where the edgewise or in-plane natural frequency was between one and two times the primary forcing frequency (rotor rotational frequency equal 1P). By selecting an in-plane frequency above 1P, this completely eliminated any possibility of frequency coalescence during rotor run up. And while hinged rotors are generally designed to have such frequencies at values below 1P, it is at a significant cost of added weight and complexity through mechanical edgewise dampers installed around the hinges.
Further, although an important advantage of the hingeless rotor over the articulated rotor is the potential for improved handling qualities due to high control power and damping, additional reductions in weight, drag, loads, and complexity are needed for improved performance and reduced operating costs.